1. The Field of the Invention
The present invention relates generally to reducing failures of electronic devices. More specifically, the present invention relates to reducing failure of electronic devices caused by the effects of thermal expansion.
2. The Relevant Technology
Thermal expansion is the tendency of solid objects to increase in length or volume when heated. The amount of expansion typically varies depending on a material's coefficient of thermal expansion (CTE). Different types of materials have defined rates of expansion. For example, plastics typically expand as much as 10 times more than metals, which expand more than ceramics and glass. Different types of materials also have different mechanical properties, such as strength, rigidity, and modulus of elasticity. Different types of materials also have different optical properties, such as translucence and refractivity.
Many electronic devices include plastics. Because plastics expand much more than other materials they can cause stresses on other portions of the device coupled to, or encased within, the plastic. The stresses caused by expansion of the plastic can often cause failure of the electronic device. An electronic device can include silicon based components, metallic leads, thin glass portions, trenches, grooves, or other features that may be particularly prone to cracking. Thus, in these instances, even a slight expansion by adjacent portions of the device can cause failure of the electronic device.
Often, however, plastics are used to protect electronic components within a device. For example, electronic components are often encased within a molded plastic portion to protect the electronic component from its operating environment. In the case of electronic devices for transmitting or receiving optical signals, the molded plastic portion may be at least partially translucent and allow for transmission of light through the molded plastic portion. In addition, lenses, interfaces, and other portions of the device can be created as part of the molded plastic portion.
The molded plastic portion may be designed to provide a level of protection for an electronic component of the device, but the thermal expansion of the molded plastic portion can also cause failure of the electronic component. One way that failure can occur is by cracking of the electrical leads that couple the electronic component to an external electrical source. This is particularly likely where the electrical leads are encased within the molded plastic portion and the electrical leads are subjected to the stresses caused by thermal expansion of the molded plastic portion.
In some instances combinations of materials having different mechanical and/or optical properties have been used to mitigate the undesirable thermal expansion properties. These materials and combination of materials have not, however, prevented damage to the electronic component caused by thermal expansion in many instances. In addition, in many more fragile electronic components, such as those incorporating optical devices, there is an even greater need to improve reliability and reduce damage caused by thermal expansion. Moreover, some electronic devices operate in environments where greater variations in temperature are experienced thereby causing greater changes in expansion of the various materials of the electronic device. Thus, what would be advantageous is to reduce the damaging effects of thermal expansion to components of an electronic device. What would also be advantageous is to reduce the damaging effects of thermal expansion while improving optical transmission characteristics of an optical electronic device.